1. Field of the Invention
The present invention relates to a nuclear power plant and an operation method thereof, and particularly, to augmenting a power generation capacity.
2. Description of the Related Art
In a conventional newly-constructed nuclear power plant, a power output is augmented by, for example, improving either of a composition or a shape configuration of a fuel assembly, or the like, and by increasing a main steam flow rate at an outlet of a reactor.
A technology of such a conventional example is disclosed in Japanese Patent Laid-Open Publication Hei. 9-264983.
When applying the conventional technology described above to an existing nuclear power plant, the main steam flow rate increases substantially proportional to an increase of the power output. In order to suppress an increase of the main steam flow rate, a feedwater temperature may be lowered; however, if an extraction steam for heating the feedwater is simply decreased, thermal efficiency is extensively deteriorated and the power output hardly increases. This is not realistic option. Further, the increase of the main steam flow rate decreases a design margin of pressure vessel internals such as feedwater piping, a feedwater heater, a feedwater pump, and a steam dryer, and almost all power plant components, such as a main steam pipe, a high pressure turbine, a low pressure turbine, and a condenser. In a power plant using a normal boiling water reactor, the high pressure turbine is one of the components most likely to be the first to lose its design margin due to the increase of the main steam flow rate. Also in a nuclear power plant system other than a boiling water reactor, there is a similar problem with respect to a plant having a comparatively small design margin of the high pressure turbine, such that when applying a conventional technology to augment power output to an existing nuclear power plant, large scale improvement and change of the plant instruments is required.
Consequently, there is a need for a nuclear power plant and operation method thereof that enable a power uprate of the plant without extensively changing a configuration of the plant, including its instruments.